• Journal of the korean Society of Automotive Engineers
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• v.15 no.2
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• pp.121-129
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• 1993

Plane strain punch stretching test (PSST) was developed to evaluate stamping formability of sheet materials. In this test, the rectangular specimen of sheet material is uniformly stretched up to fracture by raising a specially designed punch to certainly assure plane strain stretching deformation along the longitudinal direction of the specimen. The stamping formability was evaluated by limit punch height(LPH) in plane strain punch stretching test compared to limit dome height(LDH) in hemispherical punch stretching test. LPH-value in PSST well ranks the stamping formability of various material and correlates with press performance. Moreover by using ultrasonic thickness gauge the plane strain intercept-limit plane strain(FLCo)-in forming limit curve can be accurately determined from thickness measurement around the fracture area. The FLCo derived from thickness measurement well correlates with the results from circle grid analysis for the deformed circle grid marked on the surface of the specimen.

• Transactions of Materials Processing
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• v.7 no.6
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• pp.539-544
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• 1998

Hemi-spheroidal punch stretching test was developed to evaluate the press formability of sheet materials. In the plane strain stretching tests our specially designed hemi-spheroidal head punch were used. In the experiment the circular sheet blanks with parallel edge sides are uniformly stretched up to fracture by raising these punches to assure plane strain stretching deformation along the longitudinal direction of the specimens. The press formability was evaluated by limit punch height(LPH) and minor strain mea-surement around the fracture area. Compared with the hemi-spherical punch and the hemi-cylindrical one our hemi-spheroidal punch was more useful in the experimental reproduction and reliance for press formability test.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.62-65
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• 2001

The effects of the initial torture of workpiece as well as the process conditions such as punch speed and lubrication on the formablity of sheet stretching are investigated by experiments. Two types of the initial textures of aluminum sheet plane strain compression torture and recrystallization texture are chosen since those are the most common in practice. Punch loads vs depth and thickness strain distributions along radial directions having the slope of $0^{\circ},\;45^{\circ},\;90^{\circ}$ with rolling directions are reported for hemishperical punch stretchings under a variety of process conditions.

• Transactions of Materials Processing
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• v.27 no.5
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• pp.301-313
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• 2018

In this paper, tensile test was performed on pure titanium sheet (CP Ti sheet) with HCP structure in each direction to evaluate mechanical and surface properties and analyze microstructural changes during plastic deformation. We also evaluated forming limits of Ti direction in dome-type punch stretching test using a non-contact three-dimensional optical measurement system. As a result, it was revealed the pure titanium sheet has strong anisotropic property in yield stress, stress-strain curve and anisotropy coefficient according to direction. It was revealed that twinning occurred when the pure titanium sheet was plastic deformed, and tendency depends differently on direction and deformation mode. Moreover, this seems to affect the physical properties and deformation of the material. In addition, it was revealed the pure titanium sheet had different surface roughness changes in 0 degree direction and 90 degree direction due to large difference of anisotropy, and this affects the forming limit. It was revealed the forming limit of each direction obtained through the punch stretching test gave higher value in 90 degree direction compared with forming limit in 0 degree direction.

• Journal of Magnetics
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• v.21 no.1
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• pp.153-158
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• 2016

This paper aims to discuss the Non Darcy boundary layer flow of non-conducting viscous fluid with magnetic ferroparticles over a permeable linearly stretching surface with ohmic dissipation and mixed convective heat transfer. A magnetic dipole is applied "a" distance below the surface of stretching sheet. The governing equations are modeled. Similarity transformation is used to convert the system of partial differential equations to a system of non-linear but ordinary differential equations. The ODEs are solved numerically. The effects of sundry parameters on the flow properties like velocity, pressure, skin-friction coefficient and Nusselt number are presented. It is deduced the frictional resistance of Lorentz force decreases with stronger electric field and the trend reverses for temperature. Skin friction coefficient increase with increase in ferromagnetic interaction parameter. Whereas, Nusselt number decrease.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.03a
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• pp.92-100
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• 1994

Forming limit diagrams for three different galvanized deep drawing quality steel sheets have been measured by hemispherical punch stretching. The experimental forming limit diagrams have been compared with results calculated using the shear instability criterion and the M-K model which takes into account a strain gradient effect resulting from bending (curvature) of a flat sheet by punch stretching. The measured data were in good agreement with the results calculated using exponent M value of 8 in Hosford's yield criterion for the M-K model and M= 6 for the shear instability model.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06a
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• pp.164-170
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• 1998

Hemi-spheroidal punch stretching test was developed to evaluate the press formability of sheet materials. In the plane strain stretching tests, our specially designed hemi-spheroidal head punch, hemi-cylindrical head punch(RIST type) and hemi-spherical head punch were used, respectively. In this experiment, the circular sheet blanks with parallel edge sides are uniformly stretched up to fracture by raising these punches to assure plane strain stretching deformation along the longitudinal direction of the specimens. The press formability was evaluated by limit punch height(LPH) and minor strain measurement around the fracture area. Compared with the hemi-spherical punch and the hemi-cylindrical one, our hemi-spheroidal punch was more useful in the experimental reproduction and reliance for press formability test.

• Transactions of Materials Processing
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• v.1 no.1
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• pp.75-86
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• 1992

Coated sheet steels have been increasingly used in automotive industry for improving corrosion resistance. One of the arised concerns is frictional behavior of coated sheet steel in stamping process. But analyses of the frictional behavior are complex and difficult. A tensile strip test has been developed for evaluating friction under the condition which simulate the stretching of sheet. Tests are conducted under different die radius and lubrication conditions. Electro-galvanized steel sheets show a lower coefficient of friction than bare steel sheets whose coated layers have been chemically removed. The coefficients of friction are independent of die radius.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06a
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• pp.121-130
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• 1998

In order to analyze the forming characteristics of laser welded tailored blanks, laser welded blanks of different thickness and strength combinations were prepared and tensile, stretching, stretch flanging and deep drawing tests were done. The tensile elongation perpendicular to the weld line, stretching and stretch flanging formability decreased with increasing the deformation restraining force (strength ${\times}$ thickness) ratio between two welded sheets. The tensile elongation along weld line reached a value above 90% of the single sheet's elongation. Stretch flanging formability was reduced to approximately 10% of the single sheet value when the deformation restraining force ratio between two welded sheets was increased to two. Weld line movement of deep drawing test specimens was also affected by the strength ratio of the combined sheets, the weld line location and forming conditions. In all forming modes of tailored blanks, excessive weld line movement resulted from strain concentrations at the weaker sheet and resulted in fracture of the weaker side.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.380-388
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• 2016

Commercially pure titanium (CP Ti) has been actively used in plate heat exchangers due to its light weight, high specific strength, and excellent corrosion resistance. However, compared with automotive steels and aluminum alloys, there has not been much research on the plastic deformation characteristics and press formability of CP Ti sheet. In this study, the mechanical properties of CP Ti sheet are clarified in relation to press formability, including anisotropic properties and the stress-strain relation. The flow curve of the true stress-true strain relation is fitted well by the Kim-Tuan hardening equation rather than the Voce and Swift models. The forming limit curve (FLC) of CP Ti sheet was experimentally evaluated as a criterion for press formability by punch stretching tests. Analytical predictions were also made via Hora's modified maximum force criterion. The predicted FLC with the Kim-Tuan hardening model and an appropriate yield function shows good correlation with the experimental results of the punch stretching test.